This invention relates to materials having a high density as are used in practical applications where conventionally high specific gravity materials such as lead have been used. More specifically, the invention relates to a malleable high density polymer material particularly useful for projectiles for firearms and angling weights.
Lead projectiles, lead shots, and angling weights are claimed to pose significant hazards. Ingestion of such lead by wildlife has been said to pose problems.
In order to avoid the use of lead, various attempts have been made to produce effective, lead-free shot pellets, bullets and angling weights.
Various approaches have been used to produce shot pellets, bullets and angling weights that are non-toxic and lead-free. Some of these are described in U.S. Pat. No. 5,786,416 to Gardner, et al; U.S. Pat. No. 4,949,645 to Hayward, et al; and U.S. Pat. No. 5,399,187 to Mravic, et al.
According to the present invention, there is provided a malleable high density polymer material comprising:
a. a high density metal component; and
b. a polymer phase consisting of a rigid or hard component, and an elastomeric modifier for the hard component, and where the elastomeric component is chosen from one of several narrow molecular weight distribution ethylene/alpha-olefin elastomers.
Accordingly, one advantage of the present invention is to achieve a surprisingly malleable, high density material that has unusual melt properties which may be used as a lead substitute in the making of for example, projectiles, shot, or angling weights.
Another advantage of the present invention is to provide a lead substitute that is non-toxic.
A malleable high density material with unusual melt processing properties may be prepared by combining a high density metal or metals with a polymer system comprising:
a. a base polyolefin such as polypropylene; and
b. a narrow molecular weight distribution ethylene/alpha-olefin elastomer such as Engage(trademark) (Dupont Dow Elastomers).
Appropriate stabilizers, compatibilizers or dispersion aids, mold release agents, etc., may also be included. By choosing non-toxic components with suitable densities, materials may be produced that have physical characteristics very similar to lead but are non-toxic and are useful for applications such as firearm projectiles (shot and bullets) and angling weights.
The use of narrow molecular weight distribution ethylene/alpha-olefin elastomer as a component in the polymer phase provides unique melt processing characteristics and malleability to the metal/polymer composites. In a molten state, these compositions exhibit very little melt flow when tested under low shear test conditions (such as an ASTM D 1238-90b, 230xc2x0 C, 2.16 kg, melt indexer) but flow surprisingly well when processed at high shear rates encountered in a normal injection molding machine. In a solid state, these compositions are highly malleable. They may be hammered, squeezed, or otherwise be formed to a desired shape without loosing the prestressed material integrity.
The high density phase or component of the composite may consist of any one of or combinations of suitably dense metals. Iron, nickel, tin, bismuth, cobalt, tungsten, and tungsten carbide are examples. These metals may be used in various states of refinement and their alloys and oxides may also be used. An important characteristic is that they be non-toxic. Useful ranges and combinations are such that, when combined with the polymer phase, the desired composite density is achieved. Generally, a target composite density for a lead substitute is in the range of 5 g/cc to 13 g/cc and preferably 8 g/cc to 12 g/cc. A corresponding metal phase weight percentage would then be about 70% to 96%.
The polymer phase consists of a rigid or hard component, an elastomeric modifier for the hard component, and preferably, additives. The hard component is chosen for its toughness, ability to bind the high density metal phase, and compatibility with the narrow molecular weight distribution ethylene/alpha-olefin elastomer. Suitable polymers would include olefins, olefin copolymers, ethylene vinyl acetate, and other polymers compatible with narrow molecular weight distribution ethylene/alpha-olefin elastomers. Examples are polyethylene, polypropylene, and their copolymers.
The elastomeric component is chosen from one of several narrow molecular weight distribution ethylene/alpha-olefin elastomers. These polymers are generally prepared with metallocene single site constrained geometry catalyst or similar catalyst technology that provides precise control of molecular weight and chain branching as cited in U.S. Pat. Nos. 5,272,236; 5,278,272; 5,798,420; and 5,580,939. Examples of these products are the Engage(trademark) series of products sold by Dupont Dow Elastomers and Exact(trademark) products sold by Exxon Chemical Corporation. The ratio of rigid polymer to elastomer can be varied to control the melt processing characteristics and final properties of the final product. Weight ratios of rigid polymer/elastomer of about 90/10 to 30/70 are most useful. As the proportions of elastomer increase, the composite takes on more of the Theological and malleable characteristics described.
Additives that are included in the composite are those materials normally utilized in polymer formulating technology to impart desirable characteristics to the material during manufacturing, processing, and end use. Examples of these include heat stabilizers such as di-tertiary butyl phenol, oxidative stabilizers such as tris-nonylphenyl phosphite, dispersion aids such as silanes or titanates, mold release agents such as waxes and stearates.
As described above, the relative proportions of the major components of the compositions of this inventions may vary within certain preferred ranges, depending upon the physical properties of the individual material employed in the overall balance of properties required of the composition.
The compositions of this invention may be manufactured by conventional methods as are well known to persons skilled in the art. Also, because the material described may be processed by any conventional plastics forming process, it is possible to produce a variety of shapes for different uses.